I purchased a palm Z22 on craigslist classifieds: jobs, housing, personals, for sale, services, community, events, forums for $35.00 with all of the cables and charger. It runs Exbal very well and since it was so cheap if it gets wet it is not a huge expense to replace it. Exbal has two versions so you can use the Palm software or Windows version.
My recommendation is that even if you would like a fancy one that does GPS and all of the other stuff they are capable of, buy one dedicated to your shooting and then get the fancy one. Or get the TDS Nomad ($1600.00) and it will do it all.
Good luck.